A cataract is a hardened opaque portion on part of or all of the lens of an eye. Unchecked, a cataract could cause blindness and other complications. Cataract surgery is a procedure whereby the human lens is removed from the eye. In one method of cataract surgery, the hardened opaque lens is first fragmented and then aspirated out of the human eye.
A thin, delicate, clear membrane surrounds the lens. This membrane is left intact during this surgery, except for the opening in the front through which the cataractous lens is removed. Commonly, this sac is temporarily filled with viscoelastic material. Then an artificial lens to replace the human lens is inserted. This is referred to as an intraocular lens or IOL. Currently, the preference is to place the IOL in the hollow sac.
Phacoemulsification allows a surgeon to fragment and remove the cataract through a small incision in the eye. In recent years, there has been an interest in inserting the artificial implant lens into the eye through smaller and smaller wounds and even through the hole made for the phacoemulsification. This would allow replacement of the removed lens portion without enlarging the incision.
Cataract-replacing lens parts are commonly made of rigid polymethylmethacrylate (PMMA). The typical way to insert these lenses has been by using a blade or knife to enlarge the incision after the cataract has been removed and inserting the IOL. Since these IOLs are rigid, they require a larger incision. Larger incisions, however, require a longer recovery time and provide more probability of infection and more unstable post operative refractions. In more recent years, foldable intraocular lenses have been replacing rigid PMMA lenses.
Foldable lenses include three-piece looped designs, and a one piece plate design. The one-piece lens can be folded into a cylinder or a sphere. The folded lens can be inserted through the hole that has been used to remove the cataract ("the phaco hole"), into the eye. The artificial lens, if properly delivered, unfolds and takes the place of the removed human lens.
The artificial lens is often delivered as shown in FIG. 25. The folded lens 1000 is located in cassette 1002. The entire cassette, including the lens, is inserted into a chamber 1004 of the delivery device.
While looking through a microscope, the surgeon holds the handle part 1010, and inserts the end 1006 of the delivery device into the eye through the phaco hole. While still looking through the microscope, the surgeon reaches around with the other hand that is not holding the portion 1010 and actuates the control knob 1012. This actuation may be a screw movement or a pushing movement.
This puts the surgeon in an uncomfortable position while doing this crucial and exacting work. Specifically, the surgeon must operate the delivery device with both hands, one of which is placed in an unnatural and uncomfortable position due to an intervening optical microscope. In addition to the uncomfortable position, the surgeon's actuation of the control knob 1012 also may cause movement of the delivery end 1006 in the eye. These lenses, especially of the plate variety, must be inserted into the hollow sac occupied by the cataractous lens. This can produce a difficult situation, where the lens must be removed from the patient's eye or worse, can lead to serious postoperative vision problems.
Another problem is that sometimes the lens gets stuck as it leaves the cassette 1002, or the push rod jumps over the folded IOL and gets stuck half way out of the cassette. When this happens, the surgeon must decide how to remove the entire unit--possibly with a partially inserted lens--from the eye. The present invention, while not completely solving this problem, describes an arrangement which is far superior. The cassette can be easily detached from the inserter, leaving the IOL and cassette in the wound. Forceps can then be inserted and the IOL removed through the cassette without enlarging the wound or making other incisions to "lead" or pull the IOL out of the cassette, remove the cassette, then remove the IOL.
The inventors wondered why such a system had not been previously mechanized. They decided that there would be significant advantages to such a make a mechanized system.
The inventors found unexpectedly, however, that all commercially-available motors and actuators were unsuitable for the purpose. They found that rotary motors, e.g. those that produce a rotational force, were unsuitable in that they produced a torque on start up that could move the delivery tip, and hence increase failure rate. Also, most motors of this type were too large in size and mass, and would not fit within a conventional lens delivery device. The smaller motors that exist either could not produce enough force to push the IOL out of the cassette, or produced an unacceptable amount of heat which could cause danger for the surgeon or patient, or lacked very precise linear control. In addition, so-called micro motors are high speed and low torque. They require substantial gear reduction as well as conversion of rotary motion to linear displacement. This complexity adds to cost, increases weight and decreases reliability. If simply attached to the distal end of the device, it would be imbalanced. Linear actuators were also too large, not balanced, and consumed too much power.
To solve these problems, the inventors devised a special linear actuator that was small, balanced, produced no rotary torque, had a small power consumption, was very precise and controlled, and for the first time was practical for attachment to deliver a folded lens into an eye, through a small incision.
In view of the above, the inventors have invented a new method and apparatus for delivering an IOL into the eye. This technique uses a cassette-held folded lens, driven by a special linear actuator which produces virtually no torque on movement, produces very little heat and has a low weight. The preferred device uses the expansion and contraction of a member to deliver the force to press the lens along a path.
In addition, while doing so, the present invention obtains significant operational advantages.
The specific kind of linear actuator uses the shape change of piezoelectric materials that occurs when voltage is applied thereacross to generate linear motion.